1. Field of the Invention
The present invention relates to a die bonding apparatus equipped with a position correcting stage which corrects the position of a die to be placed thereon.
2. Prior Art
In a die bonding apparatus, a die is picked up from a wafer or tray by way of vacuum-chucking performed by a collet which is installed in a die conveying device; and the die is conveyed and placed on a position correcting stage. When the die is placed on the position correcting stage, the position (attitude) of the die is corrected by the position correcting stage. So as to prevent excessive forces or shocks from being applied to the die when the die is chucked and placed on the position correcting stage by the collet, the collet is made of a rubber or urethane material, etc. and conforms to the shape of the die. On the other hand, the die carrying surface of the position correcting stage is made of metal; and when the die is to be placed on this surface, the collet that chucks the die is moved to a point above the die carrying surface and then lowered at a slow speed, releasing the die on the die carrying surface.
Die bonding apparatuses of this type are described in, for instance, Japanese Patent Application Laid-Open (Kokai) Nos. S50-102268, S55-48942, H4-312936, and H7-211733. Japanese Utility Model Application Laid-Open (Kokai) No. S56-126844 and Japanese Utility Model Application Publication (Kokoku) No. S56-51322, etc. also disclose the above-described types of die bonding apparatuses.
In these die bonding apparatuses, if a die is inclined with respect to the die carrying surface when the die is about to be placed on the die carrying surface, the comer portions of the die may contact the die carrying surface, causing cracking and chipping in the die. Accordingly, so as to avoid this, an adjustment operation known as "parallel positioning" is performed. In this parallel positioning, the tip end surface of the collet of the die conveying device (that contacts the die) and the die carrying surface are brought so as to be parallel to each other.
The parallel positioning adjustment is generally performed in the following manner:
(1) A pressure-sensitive paper which changes color at the point where the pressure is applied is set on the die carrying surface. In this case, so as to bring the collet and pressure-sensitive paper into contact with each other, the height of the die carrying surface is raised by an amount equal to the thickness of the die+.alpha. (.alpha. is the amount of pressure used to cause a transfer to the pressure-sensitive paper), or the height position of the collet, at the time when the die is placed on the die carrying surface, is lowered by an amount equal to the thickness of the die+.alpha..
(2) The die conveying device is operated so that the same operation as that performed when a die is actually placed on the die carrying surface is performed. With this operation, the points of contact on the collet is transferred to or marked on the pressure-sensitive paper.
(3) The inclination of the collet, if any, is adjusted so that the shape duplicated on or transferred to the pressure-sensitive paper is a more or less uniform shape.
(4) The operations of (1) through (3) are repeated until the shape of the collet is uniformly transferred to the pressure-sensitive paper.
Thus, in the prior art, the shape of a collet is acquired (transferred) by means of pressure-sensitive paper when the parallel positioning adjustment operation is performed. Accordingly, the height of the position correcting stage must be raised or lowered beforehand; and therefore, the position correcting stage must be returned to its original position after the adjustment.
In the meantime, the amount the position correcting stage is raised or the amount the height of the collet is lowered must be an amount which is sufficient to obtain a clear transfer of the shape of the collet to the pressure-sensitive paper. Accordingly, an appropriate pressure needed for the transfer (that corresponds to the above-described .alpha.) cannot be obtained unless the operations (1) through (3) are repeated several times.
In addition, the sensitivity of the pressure-sensitive paper is generally not quite accurate; and even if the transferred shape appears to be uniform, there is actually still a considerable amount of inclination of the collet in most cases.
If cracking or chipping occurs in the die even though the above-described adjustment operation of (1) through (3) is performed, then it is necessary to perform a further adjustment which would prevent cracking or chipping according to the experience and intuition of the operator and to conduct test bonding; and this operation is repeated until favorable results are obtained. Thus, numerous dies and lead frames, etc. are consumed in the test bonding which are eventually wasted.
As seen from the above, in the prior art, the operating characteristics are poor and considerable experience is required.